Ch.20 Notes Mc Neely 2010


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Ch.20 Notes Mc Neely 2010

  1. 1. Ch. 20: Weather Patterns & Severe Storms Earth-Space Science Bremen High School Teacher : Aaron McNeely Arizona monsoon storm from Kitt Peak Observatory
  2. 2. Air Masses <ul><li>An air mass is an immense body of air that has similar temperatures and humidity throughout </li></ul><ul><li>Homogenous </li></ul><ul><li>Produce “air mass weather”, similar conditions for a few days of time </li></ul>
  3. 3. Classifying Air Masses <ul><li>The area over which an air mass gets its characteristic temperature and humidity is called its source region </li></ul><ul><li>Air masses are named according to their source region and temperature </li></ul>
  4. 4. Source Regions <ul><li>Polar (P) air masses form at high latitudes toward earth’s poles </li></ul><ul><li>Tropical (T) air masses form at low latitudes closer to earth’s equator </li></ul>
  5. 5. Maritime and Continental <ul><li>Surfaces : Land or water </li></ul><ul><li>Continental (c) air masses form over land </li></ul><ul><li>Maritime (m) air masses form over water </li></ul>
  6. 6. Air Masses Polar (P) (cold) Tropical (T) (warm) Continental (c) (land) cP (land, cold) cT (land, warm) Maritime (m) (water) mP (water, cold) mT (water, warm)
  7. 7. North American Air Masses Air masses are classified by the region over which they form Nor’easters SW monsoons Indian Summer
  8. 8. Lake Effect Snow <ul><li>When cP air masses move over warmer lake water (Great Lakes), the air mass draws heat and moisture from the lake and precipitates it as lake effect snow on the leeward shores </li></ul><ul><li>Leeward cities such as Rochester and Buffalo, New York are among the snowiest in the country </li></ul>
  9. 9. Great Lakes Lake Effect <ul><li>NASA Satellite view (12-5-00) of lake effect snow over Michigan and Northern Indiana </li></ul><ul><li>Where is Bremen? </li></ul>
  10. 10. SW Monsoons <ul><li>The monsoons occur in Southern California, Arizona, and New Mexico during midsummer </li></ul><ul><li>mT air masses moving inland from over the ocean bring warm, moist air with storms and occasional heavy precipitation </li></ul><ul><li>Despite being a desert, monsoons make Arizona one of the lightning capitals of the United States (Florida is the top lightning capital) </li></ul>
  11. 11. Arizona Monsoon
  12. 12. Indian Summer <ul><li>cT air masses form in the SW United States and Mexico during summer </li></ul><ul><li>In the fall, cT air masses can create the Indian Summer , a short period of warm weather within the cooler autumn </li></ul>
  13. 13. Fronts Sec 20.2 <ul><li>When two air masses meet, they form a front </li></ul><ul><li>A front is a boundary that separates two air masses of differing temperatures and amounts of moisture </li></ul>
  14. 14. Types of Fronts <ul><li>Types of fronts </li></ul><ul><ul><li>Warm </li></ul></ul><ul><ul><li>Cold </li></ul></ul><ul><ul><li>Stationary </li></ul></ul><ul><ul><li>Occluded </li></ul></ul>
  15. 15. Warm Fronts <ul><li>A warm front forms when warm air moves into an area formerly covered by cooler air </li></ul>(all front symbols)
  16. 16. Warm Front
  17. 17. Cold Fronts <ul><li>A cold front forms when cold, dense air moves into a region occupied by warmer air </li></ul>
  18. 18. Cold Front
  19. 19. Stationary Fronts <ul><li>Occasionally, the flow of air on either side of a front is parallel to the front </li></ul><ul><li>In such cases, the surface position of the front does not move, and a stationary front forms </li></ul>
  20. 20. Occluded Front <ul><li>When an active cold front overtakes a warm front, an occluded front forms </li></ul><ul><li>The occluded front forms when an advancing cold front wedges beneath a warm front and pushes it upward </li></ul>
  21. 21. Occluded Fronts A cold front moves toward a warm front, forcing warm air aloft A cold front merges with the warm front to form an occluded front that drops heavy rain Because occluded fronts can move slowly, light precipitation falls for many days
  22. 22. Middle-Latitude Cyclones <ul><li>Middle-latitude cyclones are the main weather producing systems for the United States </li></ul><ul><li>Low pressure </li></ul><ul><li>West to east </li></ul><ul><li>L </li></ul>
  23. 23. Cyclonic System (Low Pressure) Note the warm, cold, and occluded fronts
  24. 24. Satellite View of a Cyclone Note the counter-clockwise spiral over the continental US
  25. 25. Thunderstorms Sec 20.3 <ul><li>Thunderstorms produce lightning and thunder, and frequently gusty winds, heavy rain, and hail </li></ul><ul><li>Cumulonimbus clouds, fronts </li></ul>
  26. 26. Occurrence of Thunderstorms <ul><li>The US experiences about 100,000 thunderstorms per year mostly in the Gulf of Mexico area and Florida </li></ul><ul><li>Any part of the US experiences 30-100 thunderstorms per year </li></ul>
  27. 27. Development of Thunderstorms <ul><li>Three stages of development: </li></ul><ul><li>Cumulus stage </li></ul><ul><ul><li>Strong updrafts of moist, warm air </li></ul></ul><ul><li>Mature stage </li></ul><ul><ul><li>Heavy precipitation, most active stage </li></ul></ul><ul><li>Dissipating stage </li></ul><ul><ul><li>Down moving air dominates, storm dies </li></ul></ul>
  28. 28. Stages of Thunderstorm Development Time
  29. 29. Tornadoes <ul><li>Violent rotating windstorms </li></ul><ul><li>Column of rotating air called a vortex </li></ul><ul><li>The vortex extends downward from a cumulonimbus cloud </li></ul><ul><li>Single or multiple vortices </li></ul>
  30. 30. Occurrence of Tornadoes <ul><li>United States, tornado capital </li></ul><ul><li>About 770 tornadoes occur each year in the US </li></ul><ul><li>Most occur between April and June </li></ul><ul><li>Most tornadoes form in association with severe thunderstorms </li></ul>
  31. 31. 1925 Tri-State Tornado <ul><li>The deadliest tornado in US history occurred on March 18, 1925 </li></ul><ul><li>The Tri-State or Great Tornado killed 695 people as it raced across parts of Missouri, Illinois, and Indiana </li></ul>
  32. 32. The Great Tornado
  33. 33. Hurricanes <ul><li>Hurricanes are the most violent storms on earth </li></ul><ul><li>Generally form in the tropics </li></ul><ul><li>Whirling tropical cyclones that produce winds  75 mph </li></ul>
  34. 34. Hurricane Damage <ul><li>Destructive waves up to 45 feet high </li></ul><ul><li>Flooding </li></ul><ul><li>Heavy winds </li></ul><ul><li>Storm surges, a dome of water 40-50 miles wide that sweeps over land </li></ul><ul><li>50% of the US population lives within 50 miles of a coast </li></ul>
  35. 35. Cross-Section of an Hurricane
  36. 36. Hurricane Names <ul><li>World Meteorological Association, annual list of names </li></ul><ul><li>Names originally all short, female; Male names were introduced in 1978 </li></ul><ul><li>Names are given when a disturbance becomes a tropical storm (winds 38-74 mph) </li></ul>
  37. 37. 2008 Hurricane Names Arthur Bertha Cristobal Dolly* Edouard Fay Gustav* Hanna Ike* Josephine Kyle Laura Marco Nana * US landfall, major hurr’ Omar Paloma Rene Sally Teddy Vicky Wilfred
  38. 38. 2009 Hurricane Names Ana Bill Claudette Danny Erika Fred Grace Henri Ida Joaquin Kate Larry Mindy Nicholas Odette Peter Rose Sam Teresa Victor Wanda
  39. 39. Hurricane Katrina <ul><li>Deadliest hurricane in US history </li></ul><ul><li>1,836 deaths </li></ul><ul><li>$81.2 billion in damage, the costliest natural disaster in US history </li></ul><ul><li>Katrina flooded 80% of New Orleans, devastated other cities such as Biloxi MS and Mobile AL </li></ul>
  40. 40. Katrina—August 28, 2005 New Orleans freeway submerged Katrina NASA satellite view